The growth of local and wide area networks based on Ethernet technology has been an important driver for cabling offices and homes with structured cabling systems having multiple twisted wire pairs. The ubiquitous local area network, and the equipment which operates thereon, has led to a situation where there is often a need to attach a network operated device for which power is to be advantageously supplied by the network over the network wiring. Supplying power over the network wiring has many advantages including, but not limited to: reduced cost of installation; centralized power and power back-up; and centralized security and management.
Several patents addressed to this issue exist including: U.S. Pat. No. 6,473,608 issued to Lehr et al., whose contents are incorporated herein by reference, and U.S. Pat. No. 6,643,566 issued to Lehr et al., whose contents are incorporated herein by reference. Furthermore, a standard addressed to the issue of powering remote devices over an Ethernet based network has been published as IEEE 802.3af—2003, whose contents are incorporated herein by reference, and is referred to hereinafter as the “af” standard. A device receiving power over the network wiring is referred to as a powered device (PD) and the powering equipment delivering power into the network wiring for use by the PD is referred to as a power sourcing equipment (PSE).
Powering units are commercially available which support a single port, or a plurality of ports. For clarity, each port of a power over Ethernet (PoE) controller serving a plurality of ports is referred to as a PSE and exhibits electrical characteristics as described in the “af” standard.
A PoE controller serving a plurality of ports is preferably provided with a power management functionality which prevents powering of ports when the total power consumption of all ports drawing power is within a predetermined range of the available overall power. In an exemplary prior art embodiment this is accomplished by providing a guard band as described in U.S. Pat. No. 7,257,724 issued Aug. 17, 2004 to Lehr et al, and entitled “METHOD AND APPARATUS FOR POWER MANAGEMENT IN A LOCAL AREA NETWORK”, the entire contents of which is incorporated herein by reference. In an exemplary embodiment the guard band is equal to, or greater than, the maximum power which may be drawn by a single port, or PD, disregarding the effect of inrush current. Thus, by implementing the guard band, a PD can not be powered in a situation where powering the additional PD would bring the total utilized power to be in excess of the total available power.
The power management function of the prior art further operates to monitor the total power consumption of the system. In the event that power consumption is within the guard band limit of the total available power, no additional PDs are powered, as explained above. In the event that power consumption meets or begins to exceed the total available power, or alternatively meets or exceeds a limit set below the total available power, PDs are disabled to reduce total power consumption. Preferably, PDs are disabled while maintaining priority, thus low priority PDs are disabled first, while higher priority PDs are powered.
Each PD is connected to a unique port of a particular PoE controller, and thus disabling the port is synonymous with disabling the PD.
The above mechanism leads to a system which aggressively controls power usage to ensure that pre-set limits are never exceeded. Modern power supplies are often supplied with reserve capacity, in excess of their rated capacity, which can support excess power draw for a limited time period. The prior art system does not take into account this reserve capacity, and instead maintains an unused capacity by virtue of the guard band.
U.S. patent application Ser. No. 11/934,798 published May 15, 2008 as US 2008/0114998 A1 to Ferentz et al, entitled “REDUCED GUARD BAND FOR POWER OVER ETHERNET”, the entire contents of which are incorporated herein by reference, is addressed to a method for utilizing the unused power of the guard band. However, the method first requires disabling power from at least one of the PDs, which leads to a situation where a PD may be cut off inadvertently.
There is thus a need for an improved power management scheme overcoming at least some of the above limitations.